1. Field of the Invention
The present invention relates to a nitride semiconductor device for a light-emitting diode (LED), a laser diode (LD), or the like and, in particular, to a high-efficiency high-output vertical nitride semiconductor device and a method for manufacturing the same.
2. Description of the Related Art
Known nitride semiconductor devices for light-emitting diodes or the like include one in which an n-type semiconductor layer, an active layer, and a p-type semiconductor layer each made of nitride are laminated on a sapphire substrate one on another. Since the sapphire substrate is insulative and thus electrodes may not be removed from the side of the substrate, such a semiconductor device is a so-called horizontal nitride semiconductor device having the positive electrode and the negative electrode provided on the same surface of a nitride semiconductor layer.
In recent years, there has been an increased demand for high-efficiency high-output nitride semiconductor devices. However, high-output semiconductor devices are likely to generate a large amount of heat. Particularly, in the above horizontal nitride semiconductor device, the horizontal arrangement of the positive electrode and the negative electrode results in the horizontal flow of a current, a local increase in the current density, and an increase in the amount of heat generation. As a result, it is not possible to achieve a high efficiency and a high output with the horizontal nitride semiconductor device.
In view of the above, semiconductor device structures allowing the efficient radiation of heat from semiconductor devices have been demanded in order to achieve a high efficiency and a high output, and thus so-called vertical nitride semiconductor devices have been developed. Here, the vertical nitride semiconductor devices refer to those having a semiconductor device structure in which two electrodes are arranged in the vertical direction so as to face each other with a conductive substrate and a semiconductor layer interposed therebetween.
For example, JP 2001-007394 A describes a vertical nitride semiconductor device in which an n-GaN buffer layer, an n-AlGaN clad layer, an n-GaN guide layer, an active layer having a multiple quantum well structure made of InGaN, a p-GaN light guide layer, a p-AlGaN clad layer, and a p-GaN cap layer each serving as a semiconductor layer are laminated and bonded together on a conductive n-AlGaN single crystal substrate one on another, a p-side ohmic electrode is formed on the p-GaN cap layer, and an n-side ohmic electrode is formed on the bottom surface of the n-AlGaN single crystal substrate.
In addition, JP 2006-319311 A describes a nitride-based semiconductor light-emitting device in which a pattern surface formed on a conductive substrate, a multi-layered metal layer formed on the pattern surface, and a multi-layered semiconductor layer formed on the multi-layered metal layer are included and the areas of the principal surfaces of the multi-layered metal layer and the multi-layered semiconductor layer are smaller than that of the pattern surface. A method for manufacturing the nitride-based semiconductor light-emitting device includes bonding together a block having the conductive substrate with a groove and the small substrate-side multi-layered metal layer provided on the conductive substrate and a block having a base substrate and the multi-layered semiconductor layer and semiconductor-side multi-layered metal layer provided on the base substrate; removing the base substrate; and dividing an object obtained by boding the blocks together into chip-like pieces at a region where the semiconductor-side multi-layered metal layer and the substrate-side multi-layered metal layer are not bonded (non-bonded region).